Color negative films are a class of photosensitive materials that map the luminance (neutral) and chrominance (color) information of a scene to complementary tonal and hue polarities in the negative film. Light areas of the scene are recorded as dark areas on the color negative film, and dark areas of the scene are recorded as light areas on the color negative film. Colored areas of the scene are recorded as complementary colors in the color negative film: red is recorded as cyan, green is recorded as magenta, blue is recorded as yellow, etc. In order to render an accurate reproduction of a scene, a subsequent process is necessary to reverse the luminance and chrominance information back to those of the original scene. This subsequent process may or may not require another photosensitive material.
In the motion picture industry, there are two common subsequent processes. One such subsequent process is to optically print the color negative film onto another photosensitive material, such as Eastman Color Print Film 5386.TM., to produce a color positive image suitable for projection. Another subsequent process in the motion picture industry is to transfer the color negative film information or the color print film information into a video signal using a telecine transfer device. Various types of telecine transfer devices are described in Engineering Handbook, E. O. Fritts, Ed., 8th edition, National Association of Broadcasters, 1992, Chapter 5.8, pp. 933-946, the disclosure of which is incorporated by reference. The most popular of such devices generally employ either a flying spot scanner using photomultiplier tube detectors, or arrays of charged-coupled devices, also called CCD sensors. Telecine devices scan each negative or positive film frame transforming the transmittance at each pixel of an image into voltage. The signal processing then inverts the electrical signal in the case of a transfer made from a negative film in order to render a positive image. The signal is carefully amplified and modulated, and fed into a cathode ray tube monitor to display the image, or recorded onto magnetic tape for storage.
There is a widely accepted need in the field of color image reproduction for improvements in shadow rendition in telecine transfers. There has been particular dissatisfaction with current system's ability to reproduce shadow areas of images so that they are natural in appearance. In addition, photographers and cinematographers desire the noise level in their images to be as low as possible.
To minimize image noise in color negative films, cinematographers strive to use the slowest, finest grain stocks that lighting conditions permit. Unfortunately, in many circumstances lighting conditions cannot be altered, either because of the subject material or location constraints. The cinematographer has no choice but to use the most sensitive, albeit the noisiest, stocks available. Medium and high speed color negative stocks are often used in these applications. Film speeds of ISO 200 and greater are preferred for applications containing critical shadow detail. The only recourse for improved shadow rendition is either negative flashing or changes in scene lighting. Flashing is a burdensome process in that iterations are often required to determine what exposure/flash level combinations will give the desired results. Flashing by its very nature results in an undesirable reduction in the negative's available dynamic range. Lighting changes are similarly troublesome. Given time, financial, and equipment constraints, it is often difficult if not impossible to specifically direct auxiliary lighting to increase the exposure values of specific shadow areas.
Since noise is proportional to image density (The Theory of The Photographic Process, T. H. James, Ed., 4th edition, Macmillan Publishing Co., 1977, Chapter 21, p 625, eq. 21.101), one recourse to noise reduction is to lower image densities everywhere by overall contrast lowering. While this accomplishes noise reduction it does not improve shadow reproduction. When through telecine adjustments shadow information is presented at visible brightness levels, the accompanying midtone reproduction contrast is too flat (i.e. too low).
While color print films have been designed specifically for use in making positives for telecine transferring, use of such print films adds additional processing steps and costs to forming a telecine transfer, and image information from the color negative can be lost in the print step. Accordingly, it would be desirable to make improved telecine transfers possible directly from a color negative film.